For example, a power transmission device configured to transmit engine power of an automobile and the like to a wheel needs to transmit the power from an engine to the wheel, and simultaneously allow an angular displacement and an axial displacement due to bouncing of the vehicle during travel as well as an angular displacement for a turn of the vehicle. Therefore, in general, a driveshaft of an automobile and the like has the following structure. A plunging type constant velocity universal joint that can adapt to the angular displacement and the axial displacement is arranged on a differential gear side (inboard side), and a fixed type constant velocity universal joint that can form a large operating angle is arranged on a drive wheel side (outboard side). Both of the constant velocity universal joints are coupled to each other through intermediation of the shaft. Moreover, the constant velocity universal joint on the drive wheel side (fixed type constant velocity universal joint) is coupled to a wheel bearing device configured to rotationally support the drive wheel.
Incidentally, a need for improvement in fuel economy of the automobile has been increasing in recent years, and a decrease in weight of the wheel bearing device, which is one of automobile components, is highly demanded. Hitherto, various proposals have been made to decrease the weight of the wheel bearing device, and, simultaneously, simplification in assembly and disassembly to decrease a work cost is also strongly needed in an assembly site and a repair market of the automobile.
A wheel bearing device 1 illustrated in FIG. 1 is a typical example of a structure capable of satisfying such needs. This wheel bearing device 1 is formed into a unit, and is constructed so as to be removably mounted to a constant velocity universal joint 31. In this case, the wheel bearing device 1 mainly includes an outer member 2, a hub wheel 3, an inner ring 4, balls 5 as rolling elements, and a retainer 6. Double-row outer raceway surfaces 7, 7 are formed on an inner periphery of the outer member 2, and a vehicle body mounting flange 2a configured to be mounted to a knuckle (not shown) of a vehicle body is integrally formed on an outer periphery of the outer member 2. A wheel mounting flange 8 configured to mount a wheel (not shown) is integrally formed at one end of the hub wheel 3. An inner raceway surface 9 opposing to one of the double-row outer raceway surfaces 7, 7 of the outer member 2 and a small-diameter step portion 10 having a cylindrical shape extending in the axial direction from the inner raceway surface 9 are formed on an outer periphery of the hub wheel 3. The inner ring 4 is press-fitted to the small-diameter step portion 10, and an inner raceway surface 9 opposing to another one of the double-row outer raceway surfaces 7, 7 of the outer member 2 is formed on an outer periphery of the inner ring 4. Moreover, the hub wheel 3 and the inner ring 4 construct an inner member 11. The plurality of balls 5, 5 are built so as to be rollable between the double-row outer raceway surfaces 7, 7 of the outer member 2 and the double-row inner raceway surfaces 9, 9 of the inner member 11, and the balls 5 are received in the retainer 6. The inner ring 4 is fixed in the axial direction by a staked portion 17 formed by plastically deforming an end portion of the small-diameter step portion 10 of the hub wheel 3 radially outward. In this case, a face spline 18 is formed on an end surface of the staked portion 17.
The constant velocity universal joint 31 mainly includes an outer joint member 32, an inner joint member 33, a cage 34, and torque transmitting balls 35. The outer joint member 32 includes a cup portion 36 and a bottom portion 37 integrally formed with the cup portion 36, and a female thread portion 38 is formed on an inner periphery of the bottom portion 37. In this case, a face spline 40 is formed on a shoulder portion 39 of the bottom portion 37. The face spline 40 is brought into abutment in the axial direction against the face spline 18 formed on an end surface of the staked portion 17 of the hub wheel 3, resulting in a mutually meshed state. With this configuration, a rotation torque from the shaft (not shown) can be transmitted to the wheel mounting flange 8 through the constant velocity universal joint 31 and the hub wheel 3.
The constant velocity universal joint 31 and the wheel bearing device 1 having the configurations described above are fastened and fixed to each other in the axial direction by, for example, treadedly engaging a fastening bolt 20 with the female thread 38 on the bottom portion 37 of the outer joint member 32. With such a configuration of the unit which is removably mounted, the weight and size can be reduced, and the disassembly and assembly work can be simplified.
Incidentally, a pitch cone angle is given as one of inspection items after the manufacturing of the rotation power transmitting element of this type. As illustrated in FIG. 2, FIG. 3A, and FIG. 3B, the pitch cone angle refers to an apex angle θ of a reference surface (pitch cone PC) having a conical shape acquired by overlapping pitch circles Pc1, Pc2, . . . respectively passing through meshing positions Pe1, P2, . . . between teeth 41 constructing the one face spline 40 and teeth 19 constructing the another mating face spline 18 (see FIG. 4 described later) in a rotation axis direction of the face splines 18 and 40. The pitch cone angle θ also affects strengths of the face splines 40 and 18, and it is important to evaluate the precisions thereof.
For example, in Patent Literature 1, a method of using a gauge head of a contact-type probe is proposed as a method of measuring a tooth shape of a gear.